The invention relates to a circuit arrangement for operating a lamp comprising                input terminals for connection to the poles of a voltage supply source,        a circuit part I coupled to the input terminals for igniting the lamp and for generating a lamp current out of a supply voltage delivered by the supply voltage source,        a circuit part II, coupled to circuit part I, for detecting the presence of a lamp comprising                    a circuit part III for generating a current through an electrode of the lamp,            a circuit part IV for detecting the current through the electrode of the lamp.                        
Such a circuit arrangement is known. The current through the electrodes can be a DC current or a AC current. The circuit part III can be realized in many different ways. For instance circuit part III may comprise means for supplying a DC voltage source but may alternatively comprise a switched mode power supply such as a bridge circuit for supplying a high frequency AC current to the electrodes. In the latter case the circuit part III may comprise a transformer equipped with secondary windings that are coupled to the lamp electrodes. The circuit part II makes it possible for the circuit arrangement to check whether a lamp is actually present before attempts to ignite the lamp are made. No ignition voltage is generated in case the circuit part II detects that no lamp is present. Thereby damage to components in the circuit arrangement due to high currents and voltages is prevented. Similarly, in case a burning lamp is disconnected from the circuit arrangement or the electrode of the lamp is broken, the circuit part II detects whether a new lamp is connected to the circuit arrangement or when the lamp with the electrode failure is replaced by a new lamp. In order to make sure that the new lamp that is connected to the circuit arrangement is immediately detected and ignited, the circuit part II operates continuously. A disadvantage associated with this continuous operation, however, is that the current generated by circuit part III continuously dissipates power.